The invention relates to a pneumatically, hydraulically or electromechanically operated spring brake cylinder with an emergency release device. The brake cylinder includes a housing, in which a spring-loaded piston is axially displaceable by a piston rod, at least one spring-loaded spring, and, in the case of pneumatic or hydraulic operation, a pressure connection for admitting pressure fluid to the spring-loaded piston. The emergency release device includes an operating device and an emergency release mechanism for interrupting the transmission of force between the spring-loaded piston and the piston rod with a holding device for holding the emergency release device in a transmission condition.
From German Patent Documents DE PS 26 08 502, corresponding to U.S. Pat. No. 4,063,491, and DE PS 27 48 540, corresponding to U.S. Pat. No. 4,226,168, brake cylinders are known with emergency release devices for the interruption and the automatic return of the braking function of a spring-loaded cylinder, in which case, the emergency release lever for the emergency release must be operated or held until the accumulated spring force is completely reduced.
Although these solutions have been successful per se, when the operating or emergency release lever is not operated or held sufficiently long, at extremely low temperatures, conditions of the spring accumulator are conceivable which result only in a partial force reduction. Because of the viscosity of the lubricants, which increases with the falling temperature, the time period until the force is completely reduced is lengthened in comparison to higher temperatures. During this time period, the emergency release lever would therefore have to remain operated or held in order to completely reduce the accumulated spring force.
Here, the invention uses a different approach. The invention starts with the recognition of the present problems and, in view of these problems, has the object of further developing the spring brake cylinder of the above-mentioned type such that situations are reliably avoided in which only a partial reduction or build-up of force takes place.
The invention solves this task. The holding device for holding the emergency release device at different holding positions is supplemented by a blocking device for preventing the holding of the holding device when the spring-loaded piston is only partially released. This prevents a holding, particularly an engaging of the emergency release operation when the spring accumulator is only partially released. Thus, for the emergency release of the spring accumulator, a one-time brief operation of the emergency release lever will be sufficient because the premature engaging of the blocking mechanism is reliably prevented by the blocking device.
According to one embodiment of the invention, the blocking device comprises a locking bar which locks the emergency release mechanism of the spring accumulator in the released position until the spring accumulator is completely released or is operative again.
In a cost-effective constructively simple further development, the holding device has a detent pawl acting upon a gear wheel. However, it is also conceivable that the holding device is designed to be rotating and/or linear and/or locking and/or clamping and permits several holding positions. A spring in the transmission of force of the operation of the emergency release device in a simple manner prevents intermediate conditions of the detent pawl.
According to various embodiments of the invention, particularly the following locking bar arrangements are useful:
between the spring-loaded housing and the spring-loaded piston, or
between the piston rod and the spring-loaded piston, or
between the piston rod and the spring-loaded housing.
Additional advantageous further developments of the invention are contained herein.
In the following, essentially two different basic embodiments of the invention and the blocking devices implemented within the scope of the invention will be described in detail with reference to the drawings.